This application is a 371 of PCT/JP00/05562, filed Aug. 18, 2000.
1. Field of the Invention
The present invention relates to a polyoxytetramethylene glycol (hereinafter, simply referred to as xe2x80x9cPTMGxe2x80x9d) and a method for producing the same. More particularly, the present invention is concerned with a PTMG having not only a limited content of from 2 to 5% by weight with respect to high molecular weight PTMG molecules, wherein the high molecular weight PTMG molecules are defined as PTMG molecules having molecular weights which are at least six times as large as the number average molecular weight of all PTMG molecules, but also a very limited heteropolyacid content of from 10 to 900 ppb by weight. The present invention is also concerned with a method for producing such PTMG. The PTMG of the present invention exhibits improved properties with respect to heat resistance and low viscosity. By virtue of these improved properties, the PTMG of the present invention can be advantageously used as a raw material for a polyester elastic fiber, a polyurethane elastic fiber and the like.
2. Prior Art
PTMG is used as a raw material for, for example, a polyester elastic fiber and a polyurethane elastic fiber.
As described in Japanese Patent No. 2,525,155, in general, polyether type polymers, such as PTMG, are likely to suffer deterioration by oxidation, UV rays and heat. Thus, although PTMG exhibits excellent properties as raw materials for resins and lubricants, deterioration of such a polymer has been a problem. For example, a part of PTMG is decomposed by heat applied to the polymerization reaction or by heat generated during the polymerization reaction, and the resultant polymer product suffers discoloration and lowering of the elastic properties (such as strength and elongation), which are caused by the heat decomposition (heat deterioration) of a part of the PTMG. Therefore, there is a demand for a PTMG having excellent heat resistance.
Various stabilizers for PTMG are known in the art, but most of the stabilizers are antioxidants. In addition, it is noted that conventional stabilizers for preventing heat deterioration are unsatisfactory. Specifically, an aromatic stabilizer (Japanese Patent No. 2,525,155) is frequently used for preventing heat deterioration, but it is likely to cause discoloration of an ultimate product and it may also cause environmental pollution.
In addition, since the viscosity of PTMG is relatively high, heating of the polymerization system is necessary for producing PTMG by an economically and commercially advantageous polymerization method which employs no solvent or only a small amount of solvent. When a PTMG is produced in the absence of a solvent, heat deterioration of produced PTMG becomes a problem. Accordingly, there is a demand for PTMG having both the improved properties with respect to both heat resistance and low viscosity.
Further, the addition of the above-mentioned stabilizer has a danger of causing discoloration and lowering of the elastic properties (such as strength and elongation) of the polymer product. Therefore, there has been a strong demand for a method of producing PTMG having improved heat resistance, wherein the amount of additives, such as a stabilizer, is suppressed to a level as low as possible.
Further, PTMG having high viscosity has the following problems. When PTMG is used in a polymerization thereof with other compounds in the absence of a solvent, it becomes necessary to employ high polymerization temperatures. Even when the PTMG employed has a high heat resistance, the advantages of its high heat resistance properties are not utilized in such a polymerization as needs high temperatures.
In this situation, the present inventors have made extensive and intensive studies with a view toward developing a PTMG having improved properties with respect to both heat resistance and low viscosity. As a result, it has unexpectedly been found that, when the PTMG has not only a molecular weight distribution as narrow as 1.8 or less so that the viscosity of the PTMG becomes low, but also a content of high molecular weight PTMG molecules within a specific range (2 to 5% by weight), wherein the high molecular weight PTMG molecules are defined as being PTMG molecules having molecular weights which are at least six times as large as the number average molecular weight of all PTMG molecules, the crystalline, high molecular weight PTMG molecules contained in the PTMG do not suffer phase separation but interact with the low molecular weight PTMG molecules which are likely to suffer heat decomposition, thereby suppressing the heat decomposition of the PTMG. Such a PTMG, notwithstanding a low viscosity thereof, has high heat resistance. Further, it has unexpectedly been found that, when the PTMG contains a heteropolyacid (which is a residue of the polymerization heteropolyacid catalyst (for PTMG)) in a very small amount within a specific range, a plurality of acid groups of the heteropolyacid molecule interact with hydroxyl groups of a plurality of PTMG molecules to thereby form crosslinking sites, so that the heat resistance of the PTMG is further improved without suffering promotion of depolymerization of the PTMG.
In addition, it has unexpectedly been found that the above-mentioned PTMG having excellent properties with respect to both heat resistance and low viscosity can be effectively and efficiently obtained by a method which comprises subjecting tetrahydrofuran (THF) to a polymerization reaction in a continuous polymerization reactor with a stirrer in the presence of a heteropolyacid catalyst, in which the polymerization reaction is performed in the presence of water in an amount sufficient to form a tetrahydrofuran organic phase and an aqueous tetrahydrofuran/catalyst phase having a specific gravity of from 1.8 to 2.3, while maintaining the retention time of tetrahydrofuran in the reactor within a specific range (at 0.5 to 20 hours) and while maintaining the motive power applied to the liquid in the reactor at a specific value (1.3 kW) or more to thereby obtain a polymerization reaction mixture comprising a reaction-formed tetrahydrofuran organic phase containing a polyoxytetramethylene glycol having a number average molecular weight of from 500 to 3,000 and a reaction-formed aqueous tetrahydrofuran/catalyst phase, separating the reaction-formed tetrahydrofuran organic phase containing the polyoxytetramethylene glycol from the polymerization reaction mixture, and adjusting the heteropolyacid content of the polyoxytetramethylene glycol to a level of 10 to 900 ppb by weight.
The present invention has been completed based on the above-mentioned findings.
Accordingly, it is an object of the present invention to provide a polyoxytetramethylene glycol (PTMG) having improved properties with respect to both heat resistance and low viscosity.
It is another object of the present invention to provide a method for effectively and efficiently producing the above-mentioned PTMG having improved properties with respect to both heat resistance and low viscosity.